1. Field of Invention
The present invention relates to electrical conductor bundles, especially those called harnesses, which are hardened, that is to say shielded against electromagnetic disturbances, and which are intended to electrically connect together the various items of equipment of a complex electrical installation, the correct operation of which must be ensured, even in the case of electromagnetic disturbances. Such harnesses are, for example, used on board aircraft, ships, battle tanks, etc. The present invention also relates to a process for the production of such a bundle or harness.
2. Description of Related Art It is known that these harnesses consist of a bundle of conductors which may or may not be stranded and are divided up into several sub-bundles or branches, starting from branching nodes arranged along said bundle, and of connectors arranged on the free ends of said branches.
In order to shield them against electromagnetic disturbances, said harnesses are coated with metal sheath elements completely covering said conductors. However, such a shielding sheath has the drawback, especially due to the effect of the vibrations to which said harness are subjected, of exerting an abrasive action on the objects in contact with it. Thus, it may wear away the electrical insulation covering the conductor, which said shielding sheath surrounds, or else wear away the shielding sheath of another harness (or vice versa). It is obvious that such an abrasive action may lead to undesirable malfunctions of the installations having said harnesses.
The object of the present invention is to remedy this drawback.
For this purpose, according to the invention, the multibranched bundle of electrical conductors, provided with an electromagnetic shielding system which consists of a network of metal sheath elements surrounding said conductors and providing the electrical continuity of said shielding system, is noteworthy in that it includes at least one network of braid elements braided directly on said bundle using filaments of a wear-resistant material, so that said network of braid elements forms a protection against frictional wear liable to be exerted by said metal sheath elements.
Thus, said braid elements form a protection against the abrasive action of the metal sheath elements.
In order to protect the electrical conductors of the bundle against said sheath, such braid elements may be arranged between said conductors and said metal sheath elements.
Moreover, as a variant or in addition to the above braid elements, other braid elements may be provided which are arranged on the external surface of said metal sheath elements.
Thus, this metal sheath is prevented from exerting a wearing action on the objects with which it may be in contact and vice versa.
It will be noticed that, when a sealing product is applied to said bundle (as is usually the case), it is advantageous to do so after producing said braid elements, which then serve as reinforcement for said sealing product.
Although the filaments making up the said braid elements may be of any type, as long as they withstand the abrasive action of the metal sheath, it is preferable for these filaments to be made of a synthetic material, especially a heat-fusible material.
Thus, it is possible to secure, by partial melting, at least one of the ends of said braid elements so as to prevent unbraiding after producing said braid elements on the bundle.
For the braiding, said filaments may be in the form of a twisted or untwisted yarn or a filament roving.
Moreover, the present invention also relates to a process for the production of a multibranched bundle of electrical conductors provided with an electromagnetic shielding system which consists of a network of metal sheath elements surrounding said conductors and providing the electrical continuity of said shielding system. This process is noteworthy in that produced on said bundle is a protection against the frictional wear liable to be exerted by said metal sheath elements and in that said protection is obtained by the braiding, directly on said bundle, of at least one network of braid elements consisting of filaments of a wear-resistant material.
In a known manner, said electrical conductor bundles generally include nodes each joining three branches of said bundle. In this case, at each of said nodes, three braid elements are formed, each of them leading from one of the three branches to one of the other two, the other of said other two branches passing laterally through it and the pair of branches carrying each of said three braid elements is different from the pairs of branches carrying the other two braid elements.
In the particular case where these three branches have different cross sections, it is advantageous to start by producing a first braid element carried by the two branches having respectively the smallest and the largest cross section, and then a second braid element carried by the two branches having respectively the intermediate cross section and the smallest cross section, and finally a third braid element carried by the two branches having respectively the intermediate cross section and the largest cross section.
In addition, said first, second and third braid elements may cover, respectively, all of said branch having the smallest cross section, all of said branch having the intermediate cross section and all of said branch having the largest cross section and, partially, in the vicinity of said node, said branch having the largest cross section, said branch having the smallest cross section and said branch having the intermediate cross section.
In contrast, when two of the three branches have cross sections which are at least approximately equal, it is advantageous for one of said braid elements to cover, continuously, all of said two branches.
In order to produce such a braid element, it is possible to start by forming a free braiding tail, after which said braiding tail is laid against one of said branches of the bundle which is to carry said braid element and the braiding of said braid element is started on this latter branch.
Likewise, it is possible to end a braid element with an empty braiding tail which is laid against that one of said branches carrying said braid element, on which said braid element stops.
Thus, said braiding tails may serve to secure the beginning and/or the end of said braid elements in position on the electrical conductor bundle. For this purpose, it is sufficient to provide rings or the like in order to fix said braiding tails to the bundle. As an alternative, some of the braiding tails may be secured in position by one of the braid elements which covers them.
In order to achieve self-securing of a braid element in position, it is possible, at the beginning of the production, to start the braiding at the corresponding node, working away from it before reversing the direction of advance of the braiding in order to move back toward said node and covering the beginning of the braid element already formed and said braiding tail, so as to form a hem which positionally immobilizes said braiding tail.
Preferably, when an electrical connector is mounted on the end of one of said branches, said braid element is started with a hem, as described hereinabove, on the end-piece of said connector, through which end-piece said branch enters said connector.
In the particular case where the electrical conductor bundle is in the form of a harness having a progressively narrowing main trunk with nodes from which said branches branch off, said braid elements are preferably produced starting with the thinnest branches and ending with the thickest branches.
However, in order to benefit from an already existing adjustment of the braider producing said braid elements and thus to decrease the total braiding time, when close but not necessarily consecutive branches have approximately equal cross sections, the braiding of the corresponding braid elements is carried out consecutively.